Alzheimer's disease increasingly has become recognized as a public health problem. The prevalence of severe dementia in the U.S. is reported to be about 1.3 million cases, of which 50-60% are of the Alzheimer type. In the search for physiological markers of Alzheimer's disease, the late components of cortical event-related potentials (P3) have been investigated with conflicting results. Part of this conflict may be the result of a lack of distinction between the two components of which P3 is constituted, namely, P3a and P3b. These two constituents may represent different aspects of cognitive functioning. The proposed study will investigate latency of P3a and b in patients suffering from Alzheimer's disease and in age and sex matched controls. The Blessed Dementia Scale will be employed as a validating criterion of the disease and its severity. Our overall purpose will be to find out whether P3a or P3b latency can serve as a physiological marker in the diagnosis of Alzheimer's disease.